The present invention relates to technology for controlling a magnetic disk storage apparatus, and more particularly to technology effectively applied to motor control when power supply is stopped, for example, when power failure occurs. To be more specific, the present invention relates to technology effectively used for control of a voice coil motor that moves a magnetic head for reading and writing information from and to storage tracks on a magnetic disk in, e.g., a hard disk drive in a radial direction of the disk.
A magnetic disk storage apparatus includes a spindle motor for rotating the magnetic disk, and a voice coil motor that moves (seek operation) a magnetic head for reading and writing information from and to storage tracks on the magnetic disk in a radial direction along the surface of the disk. A hard disk drive is configured so that a magnetic head glides over a disk surface by dint of wind pressure caused by disk rotation, and if disk rotation is stopped, the magnetic head comes into contact with the disk surface, possibly damaging the disk.
Accordingly, when the disk rotation is stopped, the magnetic head is retracted to a support called a lamp placed in a standby position outside the disk. Hence, when seek operation of the head is started, the magnetic head must be moved from the lamp position to over the disk. At this time, if the magnetic head is moved too fast by the voice coil motor, the magnetic head may come into contact with a disk surface and damage the disk. Thus, conventionally, it has been common to monitor back electromotive forces of the voice coil motor to control movement speeds of the magnetic head.